A recurring issue in product applications using materials such as polymeric materials is that they tend to fail or degrade due to mechanical fatigue, mechanical impact, oxidative aging due to radiation or impurities, thermal fatigue, chemical degradation, or a combination of these processes. The degradation can lead to embrittlement of the polymer, among other adverse effects. The embrittlement and associated cracking can advance to the point that it causes product failure, which creates replacement costs. Mechanical fatigue and mechanical stress, such as that caused by dropping the object, can also lead to cracks that eventually cause failure. Thermoplastic and thermoset polymer systems used in products can be particularly susceptible to these failure modalities.
This problem is a great concern because of the widespread and intensive use in modem society of polymers in product components. For instance, polymers have a significant importance and presence in the electronics industry. Examples of applications include printed circuit board (PCB) laminates, housings, enclosures, adhesives, die attach, component packaging, and organic semi-conductors. In addition to the above-mentioned failure modes, other degradation processes, such as redox reactions or chemical diffusion, can be expected in organic semi-conductors and in electrically conductive polymers (which degrade their characteristics).
Traditional approaches to increasing the reliability of polymeric-based components and products have included a focus on suitable design enhancements and the use of incrementally improved plastics. Recently, a significant increase in the availability of so-called ‘smart” materials has occurred, which relates to materials that can sense impending failure and facilitate appropriate corrective measures to prevent extensive damage. Alternatively, if the damage has already occurred, some new material systems can purportedly self-heal the damaged structure. See, e.g., Chen, et al., “A Thermally Re-Mendable Cross-Linked Polymeric Material,” Science, Vol. 295, March 2002, pp. 1698–1702.
One recently developed process intended to impart self-healing capability to a polymer involves the incorporation of microcapsules containing a healing agent in a polymer matrix. White, S. R., et al., Nature, “Autonomic Healing of Polymer Composites,” 409, 794–797 (2001). The healing agent enclosed in the microcapsules is dicyclopentadiene (DCPD). A ruthenium polymerization agent, corresponding to CAS No. 172222-30-9, is dispersed in the polymer matrix. When a fracture occurring in the polymer matrix propagates in close proximity of the microcapsules, the associated stresses caused by the fracture rupture the microcapsules. As a consequence, the healing agent is released from the ruptured microcapsules and contacts the fracture surfaces. It also comes into contact with a polymerization agent dispersed in the polymer matrix to the extent the dispersed polymerization agent is located in the direct vicinity of the fracture and released healing agent. The polymerization agent is functionally active in the presence of moisture and air (oxygen source). When the polymerization agent contacts the self-healing agent, it promotes polymerization of the healing agent, resulting in filling of the crack planes of the fracture. This filling arrests fracture propagation and reduces the compliance of the post-fractured matrix material.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. Additionally, descriptions and details of well-known features and techniques may be omitted from the figures to avoid unnecessarily obscuring the present invention.